This application requests partial funding for the purchase of a dedicated brain Positron Emission Tomography (PET) NeuroPET scanner from PhotoDetection Systems Inc (PDS). This equipment will be part of the dedicated research PET imaging facility located within the Division of Nuclear Medicine and Molecular Imaging (NMMI) at Massachusetts General Hospital (MGH), Boston, MA. The proposed instrument will service a highly productive interdisciplinary group of 14 PHS-funded investigators (17 funded grants from NCI, NIMH, NIA, NINDS, NIBIB, NHLBI) from the MGH and the local research community (Brigham and Women's Hospital, Harvard University, Tufts University), enhancing their ability to conduct their current research programs and providing opportunities for new projects and collaborations. The PHS-funded investigators'research includes PET imaging in proton beam and radionuclide therapies, PET imaging in neurodegenerative diseases such as Alzheimer's disease, Parkinson Disease with Dementia and Lewy Body Dementia, in movement disorders and in psychiatric disorders such as obsessive compulsive disorders and post traumatic stress disorders and in lung injury and coronary artery diseases in animal models. The NeuroPET is a novel type of PET cameras, that is mobile (on wheels) and uses regular electrical power that is specifically tailored for brain imaging. It also features Cesium Iodide (CsI) detector technology with wavelength shift fiber readout that allows high sensitivity (~2X whole body PET scanners) while preserving good spatial resolution within the entire field of view. Our choice of the NeuroPET was guided by two factors: a) The need for a mobile PET scanner that would allow in-room monitoring of proton beam therapy to determine while the patient is on the proton beam therapy bed the actual proton range. To our knowledge, the NeuroPET is the only scanner with the potential to achieve in-room proton beam therapy monitoring, a revolutionary concept that this system will allow to make reality today. b) The need to replace our old Scanditronix 4096 PET scanner, which is our only scanner dedicated for brain and animal research (e.g., rabbits, monkeys) with a high sensitivity brain scanner that enables not only 18FDG and 11C-PIB imaging but dynamic neuro-receptor studies characterized with low count statistics (e.g., 11C-raclopride, 11C-altropane), as well. Our preliminary assessment of the performance of a NeuroPET prototype on loan from PDS, confirmed that NeuroPET was the instrument of choice to achieve the our goals of achieving high sensitivity PET for proton beam therapy and brain imaging.